... Operational Modal Analysis Conference (IMAC XXVII), Orlando, Florida, U.S.A. Vibration Analysis and Control – New Trends and Developments 190 The error function, erf(x) ,and the unit step ... and 2 are now zero, i.e., 120==XX . External forces are applied at co-ordinates 5 and 6 and the reactions happen at co-ordinates 1 and 2. Vibration Analysis and Control – New Trends and ... write X and Fas: ,KAUB⎧⎫⎧⎫==⎨⎬⎨⎬⎩⎭ ⎩⎭XFXFXF (7) With these subsets, Eq. (6) can be partitioned accordingly: Vibration Analysis and Control – New Trends and Developments...